The fabrication of semiconductor devices typically requires a clean environment since the presence of contaminants can reduce the yield of the fabrication process. The contaminants can prevent the proper formation of various structures and components making up a semiconductor device. For example, contaminants can prevent the creation of electrical conductors, insulators, contacts, vias, pads, and so forth, as intended. The improper formation of the various structures and components of a semiconductor device can result in the semiconductor device not being able to operate as designed or at all.
The contaminants can arise from a fabricating environment that is not sufficiently clean. In such a situation, contaminants such as dust particles in the air, dissolved and undissolved materials in fluids and solutions, defects in the materials, and so forth, can be introduced into the fabrication process. Contaminants can also arise as a result of the fabrication process itself. For example, the development of resist layers, the etching of high-K materials, and so on, can leave residual materials that if not removed, can contaminate the semiconductor wafer.
With reference now to FIGS. 1a and 1b, there are shown diagrams illustrating contaminants on a semiconductor substrate and a potential effect of contaminants on semiconductor device fabrication. The diagram shown in FIG. 1a illustrates a semiconductor substrate 100 with contaminants, such as a single contaminant 105 and a group of contaminants 106. An entirety of contaminants 107, including the single contaminant 105 and the group of contaminants 106 and others not specifically labeled, shown in FIG. 1a can be referred to as being a satellite defect.
The semiconductor substrate 100, as shown in FIG. 1a, is used in the manufacture of arrays of micromirror light modulators, also referred to as digital micromirror devices (DMD), to be used in microdisplay-based display systems. The diagram illustrates the semiconductor substrate 100 after the developing of a resist layer 110 intended to create an underlying support structure for a subsequent layer, such as a mirror of the micromirror light modulator, a hinge for the mirror, or any other type of layer. Developing a resist layer can include the exposure of the resist layer to a light (or some form of radiation) that has passed through a pattern mask, with portions of the resist layer exposed to the light (or radiation) being physically changed and then rinsing away parts of the resist layer with a developing solution. The developing of the resist layer 110 resulted in the formation of contaminants, such as the contaminant 105 and the group of contaminants 106, on the surface of the resist layer 110.
The contaminants resulting from the developing of the resist layer 110, if not removed, can be covered by subsequently-formed layers. For example, the contaminants 105 and 106 shown on the resist layer 110 can be covered by a layer of mirror material when the mirror material is deposited onto the resist layer 110. The diagram shown in FIG. 1b illustrates a layer of mirror material 150 after being deposited onto the resist layer 110, wherein the resist layer 110 has contaminants 105 on its surface. The layer of mirror material 150 will coat the contaminants 105 and will produce bumps, such as bump 155, as a result of the contaminants 105. Although shown in the context of the mirror of the micromirror light modulator, contaminants can produce bumps in other layers, wherein there is a layer of material deposited over a patterned resist layer.
The bumps 155 can negatively affect the reflectivity of the mirror formed on the resist layer 110. For example, the bumps 155 on the mirror surface can scatter light rather than accurately reflecting the light. The bumps 155 may also alter the tilt angle of the mirror if the bumps 155 are located in a position where the pivoting mirror makes contact. Furthermore, if the bumps 155 are in a hinge layer, the bumps 155 may cause a locally high electromagnetic field that can cause residue to form and cause mirror failure over time. In a display system, an important measure of the image quality is the display system's contrast ratio, which is a ratio of a brightest gray shade (typically pure white) displayable to a darkest gray shade (usually pure black) displayable. However, light scattered on the surface of the mirror due to the bumps 155 can brighten the darkest gray shade, thereby reducing the contrast ratio of the display system. Furthermore, since some of the light striking the mirror is scattered, the display system is also not capable of maximizing its brightest gray shade. Additionally, individual light modulators with mirrors with different tilt angles can cause poor image and contrast ratio uniformity across the array of micromirror light modulators.
Contaminants present in the fabricating environment can be addressed through the employment of better filtration systems to filter the air in the fabricating environment, for example. Additionally, the use of higher grade materials in the fabrication process can further reduce the number of contaminants in the fabricating environment. To eliminate contaminants arising from the fabrication process, it is possible to clean the semiconductor wafer with a cleaning fluid or solvent to remove at least some of the contaminants.
One disadvantage of the prior art is that a cleaning fluid that is capable of removing a contaminant arising from a fabrication process may be damaging to structures and/or layers of materials on the semiconductor substrate. Damage to the structures and layers already present on the semiconductor substrate can potentially be more harmful to the operation of the semiconductor devices than the negative effects of the contaminants.
Another disadvantage of the prior art is that the use of a cleaning fluid that does not damage structures and materials already present on the semiconductor substrate may not be able to remove a sufficient number of contaminants to make the cleaning process worthwhile.